Retractable lens system

ABSTRACT

A retractable lens system includes a linearly movable ring; a radially-retractable optical element supported by the linearly movable ring; an exposure control unit supported by the linearly movable ring and adjacent to the radially-retractable optical element; an exposure control unit recess formed on the exposure control unit to face the radially-retractable optical element when the radially-retractable optical element is in the radially-retracted position; a retracting device which retracts the radially-retractable optical element to the radially-retracted position and brings at least a part of a frame of the radially-retractable optical element to enter the exposure control unit recess when the linearly movable ring retracts from a ready-to-photograph position to a retracted position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a retractable lens system, moreparticularly to a retractable lens system including aradially-retractable optical element which is movable between aphotographing position on an optical axis and a radially-retractedposition eccentric from the optical axis.

2. Description of the Related Art

The assignee of the present invention has proposed a lens barrelretracting mechanism of a retractable zoom lens, which makes it possibleto achieve a remarkable reduction in length of the retractable zoom lenswhen fully retracted, in U.S. patent application Ser. No. 10/368342.This lens barrel retracting mechanism has been incorporated in digitalcameras commercially available under the trademark of “Optio S”.

The principal feature of the retractable zoom lens disclosed in theUnited States Patent Application is that an optical element of a zoomlens optical system is radially retracted from a position on a commonoptical axis of the zoom lens optical system to a different positionoutside of the optical axis, and the radially-retractable opticalelement and at least one optical element of the remaining opticalelement(s) of the zoom lens optical system are moved rearward along theoptical axis when the retractable zoom lens is fully retracted, for thepurpose of achieving a further reduction in length of the retractablezoom lens in a retracted state thereof.

More specifically, in this retractable zoom lens, a radially-retractableoptical element (e.g., a lens group) is supported by a linearly movableframe which is guided linearly in an optical axis direction so that saidradially-retractable optical element is capable of rotating about anaxis parallel to the optical axis between a photographing position onthe optical axis and a radially-retracted position (eccentric position),i.e., a position eccentric from the optical axis. This linearly movableframe is linearly moved in the optical axis direction by a torque of arotating drive member between a retracted position and aready-to-photograph position in the zooming range. A plurality ofmovable lens frames respectively supporting a plurality of lens groupswhich include the linearly movable frame are moved from their respectiveretracted positions to their ready-to-photograph positions in thezooming range by a rotation of a rotatable member rotated by the torqueof the rotating drive member. Furthermore, the retractable zoom lens isprovided with a stationary cam member which moves the aforementionedretracted optical element between the photographing position and theradially-retracted position thereof by a moving force of the linearlymovable frame in the optical axis direction relative to the stationarycam member when the linearly movable frame moves from the retractedposition to the ready-to-photograph position in the zooming range.

In this known retractable zoom lens, the space between theradially-retractable optical element and other optical elements atrespective retracted positions thereof in the optical axis direction isminimized to reduce the length of the zoom lens in the retracted statethereof. However, subsequent investigation has revealed that there isstill room for a further reduction in length of the zoom lens in theretracted state thereof.

SUMMARY OF THE INVENTION

The present invention provides a retractable lens system in which anoptical element of a photographing optical system is radially retractedfrom a position on a common optical axis of the photographing opticalsystem to a different position outside of the optical axis and theradially-retracted optical element is moved rearward along the opticalaxis from the photographing position thereof when the retractable lenssystem is retracted to a retracted position, wherein the retractablelens system has a structure making it possible to achieve furtherreduction in length of the retractable lens system when it is retractedto the retracted position.

According to the present invention, a retractable lens system isprovided, including a linearly movable ring which is guided linearly inan optical axis direction of a photographing optical system, andretracts when the retractable lens system changes from aready-to-photograph state to a retracted state; a radially-retractableoptical element of the photographing optical system, theradially-retractable optical element being supported by the linearlymovable ring to be retractable to a radially-retracted position outsideof the optical axis from a ready-to-photograph position on the opticalaxis; an exposure control unit which includes exposure control elements,and is supported by the linearly movable ring to be positioned adjacentto the radially-retractable optical element in the optical axisdirection; a recess formed on the exposure control unit to face theradially-retractable optical element when the radially-retractableoptical element is in the radially-retracted position; and a retractingdevice which retracts the radially-retractable optical element from theready-to-photograph position to the radially-retracted position alongthe exposure control unit and brings at least a part of theradially-retractable optical element to enter the recess when thelinearly movable ring retracts from a ready-to-photograph position to aretracted position.

It is desirable for the radially-retractable optical element to bepositioned behind the exposure control unit. When the linearly movablering retracts from the ready-to-photograph position to the retractedposition, a support frame which supports the radially-retractableoptical element comes into contact with a stationary member positionedbehind the radially-retractable optical element to be prevented fromfurther moving rearward, and the exposure control unit approaches theradially-retractable optical element to bring the part of theradially-retractable optical element to enter the recess.

It is desirable for the support frame, which supports theradially-retractable optical element, to be rotatable about a pivotbetween the ready-to-photograph position and the radially-retractedposition, the pivot being fixed to the linearly movable member to extendparallel to the optical axis. The support frame is movable along thepivot in a direction parallel to the optical axis.

It is desirable for the retracting device includes a stationary cam barwhich projects from the stationary member and includes a cam surface forconverting a moving force of the linearly movable ring in the opticalaxis direction into a moving force in a direction orthogonal to theoptical axis direction.

It is desirable for the stationary member, which is positioned behindthe radially-retractable optical element, to include a recess formed ona front surface of the stationary member to be aligned with the recessof the exposure control unit in the optical axis direction. At least arear end of the radially-retractable optical element is accommodated inthe recess of the stationary member when the retractable lens system isin the retracted state.

It is desirable for the exposure control unit to include an actuator fordriving the exposure control elements. The actuator is positioned on asame side of the exposure control unit as the recess so as not tooverlap a moving path of the radially-retractable optical element.

It is desirable for the exposure control elements to include at leastone diaphragm blade and at least one shutter blade which lie atdifferent respective positions in the optical axis direction, theshutter blade being positioned closer to one of front and rear surfacesof the exposure control unit on which the recess is formed than thediaphragm blade.

It is desirable for the photographing optical system to include a zoomlens system.

It is desirable for the radially-retractable optical element to bepositioned between a frontmost optical element and a rearmost opticalelement of the photographing optical system in the optical axisdirection.

It is desirable for the radially-retractable optical element to includea lens group among a plurality of movable lens groups of thephotographing optical system.

It is desirable for the retracting lens system to be incorporated in adigital camera using an image pickup device. The image pickup device ismounted to the stationary member.

It is desirable for the retractable lens system to include a cam ring,positioned around the linearly movable ring, for moving a plurality ofoptical elements of the photographing optical system which include theradially-retractable optical element in the optical axis direction whenthe cam ring is rotated.

In an embodiment, a retractable lens system of a camera is provided,including a linearly movable ring which is guided linearly in a opticalaxis direction and retracts when the retractable lens system changesfrom a ready-to-photograph state to a retracted state; a lens groupsupported by the linearly movable ring to be retractable to aradially-retracted position outside of the optical axis from aready-to-photograph position on the optical axis; an exposure controlunit which includes shutter blades, and is supported by the linearlymovable ring to be positioned adjacent to the lens group in the opticalaxis direction; a stationary member positioned behind the lens group; aretracting member which projects from the stationary member, andretracts the lens group from the ready-to-photograph position to theradially-retracted position along the exposure control unit by a forceproduced by a relative movement between the linearly movable ring andthe retracting member in the optical axis direction when the linearlymovable ring retracts from a ready-to-photograph position to a retractedposition; and a front recess and a rear recess which are formed on arear surface of the exposure control unit and a front surface of thestationary member to face a front end and a rear end of the lens group,respectively, when the lens group is in the radially-retracted position.The lens group retracted to the radially-retracted position and theexposure control unit move rearward and approach each other in theoptical axis direction to bring a front end and a rear end of the lensgroup to enter the front recess and the rear recess, respectively, whenthe linearly movable ring retracts from the ready-to-photograph positionto the retracted position.

According to the present invention, in a retractable lens system inwhich an optical element of a photographing optical system is radiallyretracted from a position on a common optical axis of the photographingoptical system to a different position outside of the optical axis, andthe radially-retracted optical element is moved rearward along theoptical axis from the photographing position thereof when theretractable lens system is retracted to a retracted position, a furtherreduction in length of the retractable lens system when retracted to theretracted position is achieved because the space between theradially-retractable optical element and the exposure control unit atrespective retracted positions thereof in the optical axis direction canbe minimized.

The present disclosure relates to subject matter contained in JapanesePatent Application No.2004-256336 (filed on Sep. 2, 2004) which isexpressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view of an embodiment of a zoom lensaccording to the present invention, showing an upper half and a lowerhalf of the zoom lens from the optical axis thereof at the wide-angleextremity and the telephoto extremity, respectively;

FIG. 2 is a longitudinal sectional view of the zoom lens shown in FIG.1, showing the upper half of the zoom lens in the retracted statethereof;

FIG. 3 is a longitudinal sectional view of a portion of a supportstructure which supports a second lens group and a third lens group ofthe zoom lens at the wide-angle extremity shown in FIG. 1;

FIG. 4 is a longitudinal sectional view of a portion of the supportstructure which supports the second lens group and the third lens groupof the zoom lens in the retracted state shown in FIG. 2;

FIG. 5 is an exploded perspective view of elements of the zoom lensshown in FIGS. 1 and 2;

FIG. 6 is an exploded perspective view of a CCD holder, a stationarybarrel and other elements of the zoom lens shown in FIGS. 1 and 2;

FIG. 7 is an exploded perspective view of a first linear guide ring, ahelicoid ring and a third external barrel of the zoom lens shown inFIGS. 1 and 2;

FIG. 8 is an exploded perspective view of a cam ring, a second linearguide ring, a second lens group moving frame and a third lens groupmoving frame of the zoom lens shown in FIGS. 1 and 2;

FIG. 9 is an exploded perspective view of the cam ring, the secondlinear guide ring, the second lens group moving frame and the third lensgroup moving frame which are shown in FIG. 8, viewed from a differentside;

FIG. 10 is an exploded perspective view of the support structure thatsupports the second lens group and the third lens group;

FIG. 11 is an exploded perspective view of a support structure thatsupports a first lens group;

FIG. 12 is a developed view of the first linear guide ring shown in FIG.7;

FIG. 13 is a developed view of the helicoid ring and the third externalbarrel which are shown in FIG. 7;

FIG. 14 is a developed view of a set of roller followers fixed to thecam ring, the first linear guide ring, the helicoid ring and the thirdexternal barrel, showing the positional relationship thereamong in theretracted state of the zoom lens;

FIG. 15 is a view similar to that of FIG. 14, showing the positionalrelationship among the set of roller followers, the first linear guidering, the helicoid ring and the third external barrel, in a state wherethe third external barrel has been slightly extended forward from theretracted state of the zoom lens;

FIG. 16 is a view similar to that of FIG. 14, showing a state where thefirst linear guide ring has been removed;

FIG. 17 is a view similar to that of FIG. 15, showing a state where thefirst linear guide ring has been removed;

FIG. 18 is a developed view of portions of the helicoid ring and thethird external barrel, showing the positional relationship between anengaging recess of the helicoid ring and engaging projections of thethird external barrel;

FIG. 19 is a view similar to that of FIG. 18, showing a state ofengagement of the engaging recess of the helicoid ring with the engagingprojections of the third external barrel;

FIG. 20 is a developed view of the cam ring;

FIG. 21 is a perspective view of a portion of the CCD holder in thevicinity of a position-control cam bar thereof;

FIG. 22 is a perspective view of the cam ring, the third lens groupmoving frame and a third lens frame (radially-retractable lens frame) ina ready-to-photograph state of the zoom lens, viewed obliquely frombehind;

FIG. 23 is a perspective view of the cam ring, the third lens groupmoving frame and the third lens frame in the retracted state of the zoomlens, viewed obliquely from behind;

FIG. 24 is a view similar to that of FIG. 23, showing the cam ring, thethird lens group moving frame, the third lens frame and an AF lens framein the retracted state of the zoom lens;

FIG. 25 is a view similar to that of FIG. 24, showing a state where thethird lens group moving frame has been radially-retracted;

FIG. 26 is a rear elevational view of the cam ring, the third lens groupmoving frame and the third lens frame in the state shown in FIG. 22, inwhich the third lens frame is held in the photographing positionthereof;

FIG. 27 is a rear elevational view of the cam ring, the third lens groupmoving frame and the third lens frame in the state shown in FIG. 23, inwhich the third lens frame is held in the radially-retracted positionthereof;

FIG. 28 is a perspective view of the third lens frame, viewed obliquelyfrom the front thereof;

FIG. 29 is a perspective view of the third lens frame, viewed obliquelyfrom behind;

FIG. 30 is a perspective view of the third lens frame, viewed obliquelyfrom behind from an angle different from the angle of FIG. 29;

FIG. 31 is a perspective view of a shutter unit of the zoom lens shownin FIGS. 1 and 2, viewed obliquely from the front thereof;

FIG. 32 is a perspective view of the shutter unit, viewed obliquely frombehind;

FIG. 33 is a cross sectional view of the third lens frame, the shutterunit and the CCD holder at positions just before reaching respectivefully-retracted positions thereof, showing the positional relationshipthereamong; and

FIG. 34 is a cross sectional view of the third lens frame, the shutterunit and the CCD holder in a state where the retracting operation of theretractable zoom lens has been completed, showing the positionalrelationship thereamong.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 show an embodiment of a zoom lens according to the presentinvention in different states. An upper half of the zoom lens 10 from anoptical axis of a photographing optical system of the zoom lens 10 shownin FIG. 1 shows a state of the zoom lens 10 at the wide-angle extremity,a lower half of the zoom lens 10 from the optical axis of thephotographing optical system of the zoom lens 10 shown in FIG. 1 shows astate of the zoom lens 10 at the telephoto extremity, and FIG. 2 shows astate of the zoom lens in a retracted position (fully retractedposition). The zoom lens 10 is incorporated in a digital camera (thecamera body thereof is not shown in the drawings). As shown in FIG. 1,the photographing optical system of the zoom lens 10 in aready-to-photograph state of the zoom lens 10 consists of a first lensgroup LG1, a second lens group LG2, exposure control elements S, a thirdlens group (radially-retractable optical element) LG3, a fourth lensgroup LG4, a low-pass filter (optical filter) 11, and a CCD image sensor(solid-state image pick-up device) 12. The first lens group LG1, thesecond lens group LG2 and the third lens group LG3 are driven along aphotographing optical axis Z1 in a predetermined moving manner toperform a zooming operation, while the fourth lens group L4 is drivenalong the photographing optical axis Z1 to perform a focusing operation.In the following description, the term “optical axis direction” refersto a direction parallel to the photographing optical axis Z1 unlessotherwise stated.

FIG. 5 is an exploded view of elements of the zoom lens 10, and FIGS. 6through 11 are enlarged views of these elements. The zoom lens 10 isincorporated in a camera body (not shown), and is provided with astationary barrel 13 fixed to the camera body. A CCD holder (retractingdevice/stationary member) 14 is fixed to a rear portion of thestationary barrel 13 from behind. The CCD image sensor 12 is mounted toa central portion of the CCD holder 14 to be held thereby via a CCD baseplate 15. The low-pass filter 11 is held by the CCD holder 14 to bepositioned in front of the CCD image sensor 12. An annular sealingmember 16 is installed between the lower-pass filter 11 and the CCDimage sensor 12 to seal the gap therebetween.

The zoom lens 10 is provided in the stationary barrel 13 with an AF lensframe (a fourth lens frame which supports and holds the fourth lensgroup LG4) 17 which is guided linearly in the optical axis directionwithout rotating about the photographing optical axis Z1. Specifically,the zoom lens 10 is provided with a pair of AF guide shafts 18A and 18Bwhich extend parallel to the photographing optical axis Z1 to guide theAF lens frame 17 in the optical axis direction without rotating the AFlens frame 17 about the photographing optical axis Z1. Front and rearends of each guide shaft of the pair of AF guide shafts 18A and 18B arefixed to the stationary barrel 13 and the CCD holder 14, respectively.The AF lens frame 17 is provided on radially opposite sides thereof witha pair of guide holes (guide grooves) in which the pair of AF guideshafts 18A and 18B are respectively fitted so that the AF lens frame 17is slidable on the pair of AF guide shafts 18A and 18B. Portions of thestationary barrel 13 and the CCD holder 14 which support the pair of AFguide shafts 18A and 18B project radially outwards from the outsidediameter of the stationary barrel 13, and accordingly, the pair of AFguide shafts 18A and 18B are positioned radially outside of thestationary barrel 13.

The zoom lens 10 is provided therein with an AF motor 19 which is fixedto the stationary barrel 13. The AF lens frame 17 can be moved forwardand rearward in the optical axis direction by a driving force of the AFmotor 19. A rotary drive shaft of the AF motor 19 is threaded to serveas a feed screw shaft (rotatable lead screw), and this rotary driveshaft is screwed through a female screw hole formed on an AF nut 20 (seeFIG. 6). The AF lens frame 17 is engaged with the AF nut 20 to beslidable thereon in the optical axis direction, and is biased forward inthe optical axis direction by an extension coil spring (biasing member)21, and the forward movement limit of the AF lens frame 17 is determinedvia the engagement between surfaces of the AF nut 20 and the AF lensframe 17 which are opposed to each other in the optical axis direction.A rearward movement of the AF nut 20 in the optical axis direction by arotation of the rotary drive shaft of the AF motor 19 causes the AF lensframe 17 to be pressed rearward by the AF nut 20 to be moved rearwardagainst the biasing force of the extension coil spring 21. Due to thisstructure, rotating the rotary drive shaft of AF motor 19 forward andrearward causes the AF lens frame 17 to move forward and rearward in theoptical axis direction.

The zoom lens 10 is provided with a zoom gear 22 which is supported bythe stationary barrel 13 to be rotatable on a zoom gear shaft 22 aextending parallel to the photographing optical axis Z1. Front and rearends of the zoom gear shaft 22 a are fixed to the stationary barrel 13and the CCD holder 14, respectively. The zoom gear 22 is positioned sothat the gear teeth thereof partly project radially inwards from aninner peripheral surface of the stationary barrel 13, and can be rotatedforward and reverse by a zoom motor 23 (shown conceptually by a labeledrectangle in FIG. 5).

As shown in FIG. 6, the stationary barrel 13 is provided on an innerperipheral surface thereof with a female helicoid 13 a, a set of threelinear guide grooves 13 b, a set of three inclined grooves 13 c, and aset of three rotational guide grooves 13 d. Threads of the femalehelicoid 13 a extend in a direction inclined with respect to both theoptical axis direction and a circumferential direction of the stationarybarrel 13. The set of three linear guide grooves 13 b extend parallel tothe photographing optical axis Z1. The set of three inclined grooves 13c extend parallel to the female helicoid 13 a. The set of threerotational guide grooves 13 d are formed in the vicinity of a front endof the inner peripheral surface of the stationary barrel 13 to extendalong a circumference of the stationary barrel 13 to communicate thefront ends of the set of three inclined grooves 13 c, respectively. Thefemale helicoid 13 a is not formed on a specific front area of the innerperipheral surface of the stationary barrel 13 which is positionedimmediately behind the set of three rotational guide grooves 13 d.Regarding each set of the above three sets of grooves (the set of threelinear guide grooves 13 b, the set of three inclined grooves 13 c andthe set of three rotational guide grooves 13 d), although each set ofgrooves is composed of three grooves which are arranged at differentcircumferential positions on the inner peripheral surface of thestationary lens barrel 13, only some of the three grooves appear in FIG.6.

The zoom lens 10 is provided inside the stationary barrel 13 with ahelicoid ring 25. The helicoid ring 25 is provided on an outerperipheral surface thereof with a male helicoid 25 a and a set of threerotational guide projections 25 b. The male helicoid 25 a is engagedwith the female helicoid 13 a, and the set of three rotational guideprojections 25 b are engaged in the set of three inclined grooves 13 cor the set of three rotational guide grooves 13 d, respectively. Thehelicoid ring 25 is provided on threads of the male helicoid 25 a withan annular gear 25 c which is in mesh with the zoom gear 22. Therefore,when a rotation of the zoom gear 22 is transferred to the annular gear25 c, the helicoid ring 25 moves forward or rearward in the optical axisdirection while rotating about the photographing optical axis Z1 withina predetermined range in which the male helicoid 25 a remains in meshwith the female helicoid 13 a. A forward movement of the helicoid ring25 beyond a predetermined point with respect to the stationary barrel 13causes the male helicoid 25 a to be disengaged from the female helicoid13 a so that the helicoid ring 25 rotates about the photographingoptical axis Z1 without moving in the optical axis direction relative tothe stationary barrel 13 by engagement of the set of three rotationalguide projections 25 b with the set of three rotational guide grooves 13d. In a state where the female helicoid 13 a is in mesh with the malehelicoid 25 a, the set of three rotational guide projections 25 b arepositioned in the set of three inclined grooves 13 c, respectively, andaccordingly, the set of three rotational guide projections 25 b and thefemale helicoid 13 a do not interfere with each other.

As can be appreciated from FIGS. 1 and 2, the zoom lens 10 is atelescopic type having three external telescoping barrels: a firstexternal barrel 37, a second external barrel 34 and a third externalbarrel 26, which are concentrically arranged about the photographingoptical axis Z1. The helicoid ring 25 moves together with the thirdexternal barrel 26 in the optical axis direction while rotating aboutthe photographing optical axis Z1. The helicoid ring 25 is provided, onan inner peripheral surface thereof at three different circumferentialpositions on the helicoid ring 25, with three rotation transfer recesses(engaging recesses) 25 d, the front ends of which are open at the frontend of the helicoid ring 25. The third external barrel 26 is provided,at corresponding three different circumferential positions on the thirdexternal barrel 26, with three pairs of rotation transfer projections(engaging projections) 26 a which project rearward from the rear end ofthe third external barrel 26 to be engageable in the three rotationtransfer recesses 25 d from the front thereof, respectively (see FIG.13). The three pairs of rotation transfer projections 26 a and the threerotation transfer recesses 25 d are movable relative to each other inthe direction of the photographing optical axis Z1, and are notrotatable relative to each other about the photographing optical axisZ1. Namely, the helicoid ring 25 and the third external barrel 26 rotateintegrally. The helicoid ring 25 is provided, on front faces of thethree rotational guide projections 25 b at three differentcircumferential positions on the helicoid ring 25, with a set of threeengaging recesses 25 e which are formed on an inner peripheral surfaceof the helicoid ring 25 to be open at the front end of the helicoid ring25. The third external barrel 26 is provided, at corresponding threedifferent circumferential positions on the third external barrel 26,with a set of three engaging projections 26 b which project rearwardfrom the rear end of the third external barrel 26, and which alsoproject radially outwards, to be engaged in the set of three engagingrecesses 25 e from the front thereof, respectively. The set of threeengaging projections 26 b, which are respectively engaged in the set ofthree engaging recesses 25 e, are also engaged in the set of threerotational guide grooves 13 d at a time, respectively, when the set ofthree rotational guide projections 25 b are engaged in the set of threerotational guide grooves 13 d.

The third external barrel 26 and the helicoid ring 25 are biased inopposite directions away from each other in the optical axis directionby compression coil springs (not shown). These compression coil springsare installed between the third external barrel 26 and the helicoid ring25 in a compressed fashion. Therefore, the set of three engagingprojections 26 b of the third external barrel 26 are respectivelypressed against front guide surfaces of the rotational guide grooves 13d therein by the spring force of the compression coil springs. At thesame time, the set of three rotational guide projections 25 b of thehelicoid ring 25 are respectively pressed against rear guide surfaces ofthe rotational guide grooves 13 d therein by the spring force of thecompression coil springs.

As shown in FIG. 13, the third external barrel 26 is provided on aninner peripheral surface thereof with a set of three rotation transfergrooves 26 c which extend parallel to the photographing optical axis Z1.The front end of each rotation transfer groove 26 c is closed at thefront end of the third external barrel 26, and the rear end of eachrotation transfer groove 26 c is open at the rear end of the thirdexternal barrel 26. The circumferential positions of the three rotationtransfer grooves 26 c correspond to those of the three pairs of rotationtransfer projections 26 a, respectively. More specifically, as shown inFIGS. 13, 18 and 19, each pair of rotation transfer projections 26 aconsists of a long projection 26 a 1 and a short projection 26 a 2 whichis smaller than the long projection 26 a 1 in the amount of projectionrearward in the optical axis direction, and the rear end opening of theassociated rotation transfer groove 26 c is positioned between the longprojection 26 a 1 and the short projection 26 a 2, and accordingly,surfaces of the long projection 26 a 1 and the short projection 26 a 2which are opposed to each other in a circumferential direction of thethird external barrel 26 form a part (the rear end opening) of theassociated rotation transfer groove 26 c.

On the other hand, the helicoid ring 25 is provided on an innerperipheral surface thereof with a set of three relative rotationallowing grooves 25 f which are communicatively connected with the threerotation transfer recesses 25 d, respectively. The three relativerotation allowing grooves 25 f extend circumferentially on a circleabout the photographing optical axis Z1, and one end (left end as viewedin FIG. 13) of each relative rotation allowing groove 25 f iscommunicatively connected with the associated rotation transfer recess25 d, and the other end (right end as viewed in FIG. 13) of eachrelative rotation allowing groove 25 f is formed as a closed end. In astate where the helicoid ring 25 and the third external barrel 26 arecoupled to each other, each relative rotation allowing groove 25 f iscommunicatively connected with the rear end opening (the right sidesurface of the associated long projection 26 a 1 as viewed in FIG. 19)of the associated rotation transfer groove 26 c so that the relativerotation allowing groove 25 f and the rotation transfer groove 26 ctogether form an L-shaped groove as shown in FIG. 19.

The zoom lens 10 is provided inside of the third external barrel 26 andthe helicoid ring 25 with a first linear guide ring 30. The helicoidring 25 is provided on an inner peripheral surface thereof with acircumferential groove 25 g which extends in a circumferential directionabout the photographing optical axis Z1, and the third external barrel26 is provided, on an inner peripheral surface thereof in the vicinityof the rear end and the front end of the third external barrel 26, witha rear circumferential groove 26 d and a front circumferential groove 26e, respectively, each of which extends in a circumferential directionabout the photographing optical axis Z1 (see FIG. 7). As shown in FIGS.7 and 12, the first linear guide ring 30 is provided on an outerperipheral surface thereof with a first plurality of relative rotationguide projections 30 a, a second plurality of relative rotation guideprojections 30 b and a third plurality of relative rotation guideprojections 30 c, in that order from the rear of the first linear guidering 30 in the optical axis direction. The first plurality of relativerotation guide projections 30 a, the second plurality of relativerotation guide projections 30 b and the third plurality of relativerotation guide projections 30 c are engaged in the circumferentialgroove 25 g, the rear circumferential groove 26 d and the frontcircumferential groove 26 e, respectively. Due to this engagement, thehelicoid ring 25 and the third external barrel 26 are supported by thefirst linear guide ring 30 to be allowed to rotate relative to the firstlinear guide ring 30 and to be prevented from moving in the optical axisdirection relative to the first linear guide ring 30. In addition, thehelicoid ring 25 and the third external barrel 26 are prevented frombeing separated totally from each other in the optical axis directionvia the first linear guide ring 30. The first linear guide ring 30 isprovided, in the vicinity of the rear end thereof at differentcircumferential positions, with a set of three linear guide projections30 d which project radially outwards. The first linear guide ring 30 isguided linearly in the optical axis direction without rotating by theengagement of the set of three linear guide projections 30 d with theset of three linear guide grooves 13 b of the stationary barrel 13.

The first linear guide ring 30 is provided with a set of three throughslots (through grooves) 30 e which radially extend through the firstlinear guide ring 30. As shown in FIG. 12, each through slot 30 eincludes a circumferential slot portion 30 e-1 which extends in acircumferential direction of the first linear guide ring 30, a firstlead slot portion 30 e-2 which extends obliquely from one end (right endas viewed in FIG. 12) of the circumferential slot portion 30 e-1, and asecond lead slot portion 30 e-3 which extends obliquely from one end(right end as viewed in FIG. 12) of the first lead slot portion 30 e-2.The angle of inclination of the first lead slot portion 30 e-2 relativeto the circumferential direction of the first linear guide ring 30 isgreater than that of the second lead slot portion 30 e-3. The zoom lens10 is provided with a cam ring 31 a front part of which is fitted in thefirst external barrel 37. A set of three roller followers 32 fixed to anouter peripheral surface of the cam ring 31 at different circumferentialpositions thereon are engaged in the set of three through slots 30 e,respectively. The set of three roller followers 32 are further engagedin the set of three rotation transfer grooves 26 c (or the set of threerelative rotation allowing grooves 25 f) through the set of threethrough slots 30 e, respectively.

Advancing operations of movable elements of the zoom lens 10 from thestationary barrel 13 to the cam ring 31 will be discussed hereinafter.Rotating the zoom gear 22 in a lens barrel advancing direction by thezoom motor 23 causes the helicoid ring 25 to move forward while rotatingdue to engagement of the female helicoid 13 a with the male helicoid 25a. This rotation of the helicoid ring 25 causes the third externalbarrel 26 to move forward together with the helicoid ring 25 whilerotating together with the helicoid ring 25, and further causes thefirst linear guide ring 30 to move forward together with the helicoidring 25 and the third external barrel 26 because each of the helicoidring 25 and the third external barrel 26 is coupled to the first linearguide ring 30, to allow respective relative rotations between the thirdexternal barrel 26 and the first linear guide ring 30 and between thehelicoid ring 25 and the first linear guide ring 30 and to be movabletogether along a direction of a common rotational axis (i.e., thephotographing optical axis Z1), due to the engagement of the firstplurality of relative rotation guide projections 30 a with thecircumferential groove 25 g, the engagement of the second plurality ofrelative rotation guide projections 30 b with the rear circumferentialgroove 26 d, and the engagement of the third plurality of relativerotation guide projections 30 c with the front circumferential groove 26e.

In the retracted state of the zoom lens 10, the set of three rollerfollowers 32 are engaged in the circumferential slot portions 30 e-1 ofthe set of three through slots 30 e, respectively, and are furtherengaged in the three relative rotation allowing grooves 25 f at closedend portions 32-K1 thereof (see FIG. 19), respectively, as shown inFIGS. 14 and 16. FIGS. 14 and 16 show the same states, although thefirst linear guide ring 30 is removed in FIG. 16 except the set of threethrough slots 30 e for the purpose of making the operation of eachroller follower 32 easier to be seen in the drawing. In addition, inFIGS. 14 and 16, the first linear guide ring 30 (the set of threethrough slots 30 e) are shown by solid lines though actually positioneda hidden position below (radially inside) the helicoid ring 25 and thethird external barrel 26.

When the helicoid ring 25 and the third external barrel 26 are movedforward while rotating, this rotation of the helicoid ring 25 and thethird external barrel 26 is not transferred to the cam ring 31 in aninitial stage of the forward movement of the helicoid ring 25 and thethird external barrel 26 because the set of three roller followers 32are engaged in the set of three relative rotation allowing grooves 25 f,respectively. The set of three roller followers 32 move together withthe helicoid ring 25, the third external barrel 26 and the first linearguide ring 30 in the optical axis direction due to the engagement of theset of three roller followers 32 with the circumferential slot portions30 e-1 of the set of three through slots 30 e, respectively.Accordingly, in an initial stage of the advancing operation of the zoomlens 10 from the retracted state of the zoom lens 10, the cam ring 31 ismoved forward in the optical axis direction without rotating.

FIGS. 15 and 17 show a state of the helicoid ring 25 and the thirdexternal barrel 26 which have been rotated by an angle of approximately30 degrees from their respective retracted positions from the retractedstate of the zoom lens 10 shown in FIGS. 14 and 16. In the state shownin FIGS. 15 and 17, each roller follower 32 is engaged in anintersection 32-K2 (see FIG. 19) of the associated relative rotationallowing groove 25 f and the associated rotation transfer groove 26 c sothat the rotation of the helicoid ring 25 and the third external barrel26 can be transferred to the roller follower 32 via a side surface (leftsurface as viewed in FIG. 19) of the rotation transfer groove 26 c atthe left end of the relative rotation allowing groove 25 f. A furtherforward movement of the helicoid ring 25 and the third external barrel26 while rotating causes each roller follower 32 to be moved rightwardas viewed in FIGS. 15 and 17 from the circumferential slot portions 30e-1 to the first lead slot portion 30 e-2 of the associated through slot30 e. Since the first lead slot portion 30 e-2 of each through slot 30 eis inclined to the circumferential direction of the first linear guidering 30 in a manner to approach the front end (upper end as viewed inFIG. 15) of the first linear guide ring 30 in a direction away from thecircumferential slot portions 30 e-1 of the associated through slot 30e, a forward movement of each roller follower 32 in the first lead slotportion 30 e-2 of the associated through slot 30 e causes the rollerfollower 32 to be disengaged from the associated relative rotationallowing groove 25 f to be engaged in the associated rotation transfergroove 26 c (i.e., the roller follower 32 is led from the associatedrelative rotation allowing groove 25 f to the associated rotationtransfer groove 26 c). In a state where the set of three rollerfollowers 32 are engaged in the set of three rotation transfer grooves26 c, respectively, the torque (rotating force) of the third externalbarrel 26 is transferred to the cam ring 31 via the engagement of theset of three roller followers 32 with the set of three rotation transfergrooves 26 c whenever the third external barrel 26 rotates. Thereupon,the cam ring 31 moves forward while rotating relative to the firstlinear guide ring 30 in accordance with contours of the first lead slotportions 30 e-2 of the set of three through slots 30 e. At this time,each roller follower 32 moves forward in the optical axis direction inthe associated rotation transfer groove 26 c while receiving a torquefrom the same rotation transfer groove 26 c. Since the first linearguide ring 30 itself has linearly moved forward together with thehelicoid ring 25 and the third external barrel 26 as described above,the cam ring 31 moves forward in the optical axis direction by aresultant amount of movement corresponding to the sum of the amount ofthe forward movement of the first linear guide ring 30 (and the helicoidring 25 and the third external barrel 26) and the amount of the forwardmovement of the cam ring 31 via the engagement of the set of threeroller followers 32 with the first lead slot portions 30 e-2 of the setof three through slots 30 e, respectively.

The above described rotating-advancing operations of the helicoid ring25 and the third external barrel 26 are performed only when the malehelicoid 25 a and the female helicoid 13 a are engaged with each other.At this time, the set of three rotational guide projections 25 b aremoving in the set of three inclined grooves 13 c, respectively. When thehelicoid ring 25 is moved forward by a predetermined amount of movement,the male helicoid 25 a and the female helicoid 13 a are disengaged fromeach other so that the set of three rotational guide projections 25 bmove from the set of three inclined grooves 13 c into the set of threerotational guide grooves 13 d, respectively. Since the helicoid ring 25does not move in the optical axis direction relative to the stationarybarrel 13 even if rotating upon the disengagement of the male helicoid25 a from the female helicoid 13 a, the helicoid ring 25 and the thirdexternal barrel 26 rotate at respective axial fixed positions thereofwithout moving in the optical axis direction due to the slidableengagement of the set of three rotational guide projections 25 b withthe set of three rotational guide grooves 13 d.

Furthermore, after a lapse of a predetermined period of time from themoment at which the set of three rotational guide projections 25 b slideinto the set of three rotational guide grooves 13 d from the set ofthree inclined grooves 13 c, respectively, the set of three rollerfollowers 32 enter the second lead slot portions 30 e-3 from the firstlead slot portions 30 e-2 of the set of three through slots 30 e,respectively. Since the second lead slot portion 30 e-3 of each throughslot 30 e is inclined to the first linear guide ring 30 in a directionaway from the associated first lead slot portion 30 e-2 and approachingthe front end (upper end as viewed in FIG. 15) of the first linear guidering 30, further rotation of the helicoid ring 25 and the third externalbarrel 26 at respective axial fixed positions thereof in a lens barreladvancing direction causes each roller follower 32 to move forward inthe second lead slot portion 30 e-3 of the associated through slot 30 e.Namely, the cam ring 31 is moved forward while rotating relative to thefirst linear guide ring 30 in accordance with contours of the secondlead slot portions 30 e-3 of the set of three through slots 30 e. Thehelicoid ring 25 and the third external barrel 26 serve as a rotatingdrive member which transfers torque to the cam ring 31 via theengagement of the set of three roller followers 32 with the set of threethrough slots 30 e and the engagement of the set of three rollerfollowers 32 with the set of three rotation transfer grooves 26 c.

Rotating the zoom gear 22 in a lens barrel retracting direction thereofvia the zoom motor 23 causes the aforementioned movable elements of thezoom lens 10 from the stationary barrel 13 to the cam ring 31 to operatein the reverse manner to the above described advancing operations. Inthis reverse operation, the helicoid ring 25 and the third externalbarrel 26 which rotate at respective axial fixed positions thereof moverearward in the optical axis direction while rotating after the malehelicoid 25 a and the female helicoid 13 a are engaged with each other.The first linear guide ring 30 linearly moves in the optical axisdirection without rotating at all times while following the rearwardlinear movement of the helicoid ring 25 and the third external barrel26. When the set of three roller followers 32 are engaged in the firstlead slot portions 30 e-2 or the second lead slot portions 32 e-3 of theset of three through slots 30 e, respectively, the cam ring 31 movesrearward in the optical axis direction relative to the helicoid 25, thethird external barrel 26 and the first linear guide ring 30 by rotationof the helicoid ring 25 and the third external barrel 26 in the lensbarrel retracting direction thereof. At this time, each roller follower32 moves rearward in the optical axis direction in the associatedrotation transfer groove 26 c while receiving a torque from the samerotation transfer groove 26 c. Thereafter, upon moving into thecircumferential slot portions 30 e-1 from the first lead slot portion 30e-2 of the associated through slot 30 e, each roller follower 32 isdisengaged from the associated rotation transfer groove 26 c at the rearopening end thereof to be engaged in the associated relative rotationallowing groove 25 f. At this time, the rotation of the helicoid ring 25and the third external barrel 26 stops being transferred to the set ofthree roller followers 32, and accordingly, the cam ring 31 is movedrearward in the optical axis direction without rotating together withthe helicoid ring 25, the third external barrel 26 and the first linearguide ring 30. Each roller follower 32 moves in the associated relativerotation allowing groove 25 f, and the zoom lens 10 falls into theretracted position thereof upon each roller follower 32 reaching theclosed end (right end as viewed in FIG. 13) of the associated relativerotation allowing groove 25 f.

The structure of the zoom lens 10 radially inside of the cam ring 31will be discussed hereinafter. As shown in FIG. 7, the first linearguide ring 30 is provided on an inner peripheral surface thereof with aset of three pairs of first linear guide grooves 30 f which are formedat different circumferential positions to extend parallel to thephotographing optical axis Z1, and a set of six second linear guidegrooves 30 g which are formed at different circumferential positions toextend parallel to the photographing optical axis Z1. Each pair of firstlinear guide grooves 30 f are respectively positioned on the oppositesides of the associated second linear guide groove 30 g (every secondlinear guide groove 30 g) in a circumferential direction of the firstlinear guide ring 30. The zoom lens 10 is provided inside of the firstlinear guide ring 30 with a second linear guide ring 33. The secondlinear guide ring 33 is provided on an outer edge thereof with a set ofthree bifurcated projections 33 a (see FIG. 8) which project radiallyoutwards from a ring portion 33 b of the second linear guide ring 33.Each bifurcated projection 33 a is provided at a radially outer endthereof with a pair of radial projections which are respectively engagedin the associated pair of first linear guide grooves 30 f. On the otherhand, a set of six radial projections 34 a (see FIG. 11) which areformed on an outer peripheral surface of the second external barrel 34at a rear end thereof and project radially outwards are engaged in theset of six second linear guide grooves 30 g to be slidable therealong,respectively. Therefore, each of the second linear guide ring 33 and theset of six radial projections 34 a of the second external barrel 34 isguided in the optical axis direction via the first linear guide ring 30.The zoom lens 10 is provided inside of the cam ring 31 with a secondlens group moving frame 35 which indirectly supports and holds thesecond lens group LG2. The first external barrel 37 indirectly supportsthe first lens group LG1, and is positioned inside of the secondexternal barrel 34. The zoom lens 10 is provided radially inside of thecam ring 31 with a third lens group moving frame (linearly movable ring)36. The second linear guide ring 33 serves as a linear guide member forguiding both the second lens group moving frame 35 that supports thesecond lens group LG2 and the third lens group moving frame 36 thatsupports the third lens group LG3 linearly without rotating the secondlens group moving frame 35 and the third lens group moving frame 36,while the set of six radial projections 34 a of the second externalbarrel 34 serve as linear guide members for guiding the first externalbarrel 37 linearly without rotating.

As shown in FIGS. 8 and 9, the second linear guide ring 33 is providedon the ring portion 33 b with a set of three linear guide keys 33 cwhich project forward parallel to one another from the ring portion 33b. A discontinuous outer edge of the ring portion 33 b is engaged in adiscontinuous circumferential groove 31 a formed on an inner peripheralsurface of the cam ring 31 at the rear end thereof to be rotatable aboutthe photographing optical axis Z1 relative to the cam ring 31 and to beimmovable relative to the cam ring 31 in the optical axis direction. Theset of three linear guide keys 33 c project forward from the ringportion 33 b into the cam ring 31. The second lens group moving frame 35is provided with a corresponding set of three guide grooves 35 a inwhich the set of three linear guide keys 33 c are engaged, respectively.As shown in FIG. 9, the second lens group moving frame 35 is furtherprovided with a ring portion 35 b having its center on the photographingoptical axis Z1, and a set of three rearward projections 35 c whichproject rearward in parallel to one another from the ring portion 35 bin the optical axis direction. The aforementioned set of three linearguide grooves 35 a are formed on the set of three rearward projections35 c, respectively. The set of three rearward projections 35 c arearranged at substantially equi-angular intervals in a circumferentialdirection of the second lens group moving frame 35. The set of threerearward projections 35 c are engaged in a corresponding set of threelinear guide grooves 36 a formed on an outer peripheral surface of thethird lens group moving frame 36 at different circumferential positionsto be slidable thereon along the set of three linear guide grooves 36 a,respectively. The third lens group moving frame 36 is provided with aring portion 36 b having its center on the photographing optical axisZ1, and a set of six forward projections 36 c which project bothradially outwards from the ring portion 36 b and forward in parallel toone another from the ring portion 36 b in the optical axis direction.Each of the aforementioned set of three linear guide grooves 36 a isformed by a combination of an outer peripheral surface of the ringportion 36 b (bottom surface of the linear guide groove 36 a) and sidesurfaces of associated adjacent two forward projections 36 c on oppositesides of the outer peripheral surface of the ring portion 36 b in acircumferential direction thereof. The second lens group moving frame 35and the third lens group moving frame 36 are biased toward each other inthe optical axis direction. Due to this structure of engagement betweenthe second lens group moving frame 35 and the third lens group movingframe 36, the second lens group moving frame 35 is guided linearly inthe optical axis direction by the second linear guide ring 33, and thethird lens group moving frame 36 is guided linearly in the optical axisdirection by the second lens group moving frame 35.

As shown in FIGS. 8, 9 and 20, the cam ring 31 is provided on an innerperipheral surface thereof with a set of three front inner cam groovesCG3, and a set of three rear inner cam grooves CG2 formed behind the setof three front inner cam grooves CG3. The second lens group moving frame35 is provided on outer peripheral surfaces of the set of three rearwardprojections 35 c with a set of three rear cam followers CF2 which areengaged in the set of three rear inner cam grooves CG2 of the cam ring31, respectively. The third lens group moving frame 36 is provided onouter peripheral surfaces of three of the six forward projections 36 cwith a set of three front cam followers CF3 which are engaged in the setof three front inner cam grooves CG3 of the cam ring 31, respectively.Each of the following four sets of grooves or followers, i.e., the setof three front inner cam grooves CG3, the set of three rear inner camgrooves CG2, the set of three front cam followers CF3 and the set ofthree rear cam followers CF2, are formed at substantially equi-angularintervals in a circumferential direction about the photographing opticalaxis Z1. Since each of the second lens group moving frame 35 and thethird lens group moving frame 36 is guided linearly in the optical axisdirection directly or indirectly by the second linear guide ring 33, arotation of the cam ring 31 causes the second lens group moving frame 35and the third lens group moving frame 36 to move in the optical axisdirection in a predetermined moving manner in accordance with contoursof the set of three rear inner cam grooves CG2 and the front inner camgrooves CG3.

The zoom lens 10 is provided with a second lens frame 40 which supportsthe second lens group LG2. The second lens frame 40 is supported by thering portion 35 b of the second lens group moving frame 35 (see FIG.10). The second lens frame 40 is fixed to the ring portion 35 b of thesecond lens group moving frame 35 by the engagement of a male screwthread (adjusting screw) formed on an outer peripheral surface of thesecond lens frame 40 with a female screw thread (adjusting screw) formedon an inner peripheral surface of the second lens group moving frame 40.The male screw thread of the second lens frame 40 and the female screwthread of the second lens group moving frame 35 are formed withrespective centers thereof on the photographing optical axis Z1.Accordingly, the position of the second lens frame 40 relative to thesecond lens group moving frame 35 in the optical axis direction can beadjusted by rotating the second lens frame 40 relative to the secondlens group moving frame 35.

The zoom lens 10 is provided between the second and third lens groupsLG2 and LG3 with a shutter unit (exposure control unit) 41 including theexposure control elements S. The shutter unit 41 is positioned radiallyinside of the third lens group moving frame 36 to be supported thereby.Although the exposure control elements S that are supported by theshutter unit 41 are schematically shown in the cross sectional viewsshown in FIGS. 1 and 2, the exposure control elements S are composed ofa set of diaphragm blades S1 and a set of shutter blades S2 positionedbehind the set of diaphragm blades S1 in the optical axis direction inactually (see FIGS. 3 and 4). As shown in FIGS. 31 and 32, the shutterunit 41 is provided with a circular photographing aperture 41 a throughwhich a light bundle of an object which is to be photographed passes.The shutter unit 41 is fixed to the third lens group moving frame 36 sothat the center of the photographing aperture 41 a coincides with thephotographing optical axis Z1. The set of diaphragm blades S1 and theset of shutter blades S2 are supported by the shutter unit 41 to bemovable into and out of the photographing aperture 41 a in a planeorthogonal to the photographing optical axis Z1. The shutter unit 41,together with two actuators (a front actuator and a rear actuator) 41 band 41 c for driving the set of diaphragm blades S1 and the set ofshutter blades S2, respectively, is unitized.

The zoom lens 10 is provided inside of the third lens group moving frame36 with a third lens frame (retracting device/support frame whichsupports the radially-retractable optical element) 42 which supports andholds the third lens group LG3 to be positioned behind the shutter unit41 adjacent thereto. The third lens frame 42 is pivoted about a pivotshaft 44 which is fixed to the third lens group moving frame 36 toproject forward. The pivot shaft 44 is positioned a predetermineddistance away from the photographing optical axis Z1, and extendsparallel to the photographing optical axis Z1. The third lens frame 42is swingable about the pivot shaft 44 between a photographing positionshown in FIGS. 1, 22 and 26 where the optical axis of the third lensgroup LG3 coincides with the photographing optical axis Z1 and aradially-retracted position shown in FIGS. 2, 23, 24, 25 and 27 wherethe optical axis of the third lens group LG3 is positioned at a radiallyretracted optical axis Z2 shown in FIGS. 2 and 27). A rotation limit pin(stop pin) 46, which prevents the third lens frame 42 from rotatingclockwise as viewed in FIG. 26 beyond a predetermined point to determinethe photographing position of the third lens frame 42, is fixed to thethird lens group moving frame 36. The third lens frame 42 is biased torotate in a direction (clockwise as viewed in FIG. 26) to come intocontact with the rotation limit pin 46 by a torsion coil spring 47. Acompression coil spring 48 is fitted on the pivot shaft 44 to bias thethird lens frame 42 rearward in the optical axis direction to removebacklash between the third lens frame 42 and the third lens group movingframe 36.

The third lens frame 42 moves together with the third lens group movingframe 36 in the optical axis direction. As shown in FIGS. 6 and 21, theCCD holder 14 is provided on a front surface thereof with aposition-control cam bar (retracting device/stationary cambar/retracting member) 49 which projects forward from the CCD holder 14to be engageable with the third lens frame 42. If the third lens groupmoving frame 36 moves rearward in a retracting direction to approach theCCD holder 14, a retracting cam surface 49 a (see FIG. 21) formed on afront end surface of the position-control cam bar 49 comes into contactwith a specific portion of the third lens frame 42 to rotate the thirdlens frame 42 to the radially-retracted position. The position-controlcam bar 49 is further provided along an inner side edge thereof with aradially-retracted-position holding surface 49 b which extends rearwardfrom the retracting cam surface 49 a in a direction parallel to thephotographing optical axis Z1. The retracting operation of the thirdlens frame 42 which is performed with the position-control cam bar 49will be discussed in detail later.

As shown in FIG. 11, the second external barrel 34 is provided on aninner peripheral surface thereof with a set of three linear guidegrooves 34 b which are formed at different circumferential positions toextend parallel the photographing optical axis Z1. The first externalbarrel 37 is provided on an outer peripheral surface at the rear endthereof with a set of three engaging protrusions 37 a which are slidablyengaged in the set of three linear guide grooves 34 b, respectively.Accordingly, the first external barrel 37 is guided linearly in theoptical axis direction without rotating via the first linear guide ring30 and the second external barrel 34. The second external barrel 34 isfurther provided on an inner peripheral surface thereof in the vicinityof the rear end of the second external barrel 34 with a discontinuousinner flange 34 c which extends along a circumference of the secondexternal barrel 34. The cam ring 31 is provided on an outer peripheralsurface thereof with a discontinuous circumferential groove 31 b inwhich the discontinuous inner flange 34 c is slidably engaged so thatthe cam ring 31 is rotatable about the photographing optical axis Z1relative to the second external barrel 34 and so that the secondexternal barrel 34 is immovable in the optical axis direction relativeto the cam ring 31 (i.e., the second external barrel 34 moves togetherwith the cam ring 31 in the optical axis direction). On the other hand,the first external barrel 37 is provided on an inner peripheral surfacethereof with a set of three cam followers CF1 which project radiallyinwards, and the cam ring 31 is provided on an outer peripheral surfacethereof with a set of three outer cam grooves CG1 in which the set ofthree cam followers CF1 are slidably engaged, respectively.

The zoom lens 10 is provided inside of the first external barrel 37 witha first lens frame 51 which is supported by the first external barrel 37via a first lens group adjustment ring 50. The first lens group LG1 issupported by the first lens frame 51 to be fixed thereto. The first lensframe 51 is provided on an outer peripheral surface thereof with apartial male screw thread 51 a, and the first lens group adjustment ring50 is provided on an inner peripheral surface thereof with a partialfemale screw thread 50 a which is engaged with the male screw thread 1 a(see FIG. 11). The position of the first lens frame 51 relative to thefirst lens group adjustment ring 50 in the optical axis direction can beadjusted during assembly of the zoom lens 10 via the partial male screwthread 51 a and the partial female screw thread 50 a.

The zoom lens 10 is provided at the front end of the first externalbarrel 37 with a lens barrier mechanism 54 (see FIG. 5) whichautomatically closes a front end aperture of the zoom lens 10 when thezoom lens 10 is retracted as shown in FIG. 2 to protect the frontmostlens element of the photographing optical system of the zoom lens 10,i.e. the first lens group LG1, from getting stains and scratches thereonwhen the digital camera is not in use. The lens barrier mechanism 54 isprovided with a plurality of barrier blades (a front pair of barrierblades and a rear pair of barrier blades) 54 a. The lens barriermechanism 54 operates so that the plurality of barrier blades 54 a arefully shut in front of the first lens group LG1 in the retracted stateof the zoom lens 10 shown in FIG. 2, and are fully opened in aready-to-photograph state of the zoom lens 10 shown in FIG. 1.

A lens barrel advancing operation and a lens barrel retracting operationof the zoom lens 10 having the above described structure will bediscussed hereinafter. In the state shown in FIG. 2, in which the zoomlens 10 is in the retracted state, rotating the zoom gear 22 in the lensbarrel advancing direction by the zoom motor 23 causes a combination ofthe helicoid ring 25 and the third external barrel 26 to move forwardwhile rotating due to the engagement of the female helicoid 13 a withthe male helicoid 25 a, and further causes the first linear guide ring30 to move forward linearly together with the helicoid ring 25 and thethird external barrel 26. At this time, firstly the cam ring 31 does notrotate but only linearly moves forward together with the helicoid ring25, the third external barrel 26 and the first linear guide ring 30, andsubsequently torque is transferred to the cam ring 31 from the thirdexternal barrel 26 to move forward while rotating relative to the firstlinear guide ring 30 by the engagement of the set of roller followers 32with the first lead slot portions 30 e-2 of the set of through slots 30e after having been rotated by the aforementioned rotation of thecombination of the helicoid ring 25 and the third external barrel 26 byan angle of approximately 30 degrees. Immediately after the helicoidring 25 and the third external barrel 26 are extended forward torespective predetermined positions thereof, the male helicoid 25 a ofthe helicoid ring 25 and the female helicoid 13 a of the stationarybarrel 13 are disengaged from each other, so that the helicoid ring 25and the third external barrel 26 rotate about the photographing opticalaxis Z1 without moving in the optical axis direction due to the slidableengagement of the set of three rotational guide projections 25 b withthe set of three rotational guide grooves 13 d. After a lapse of apredetermined period of time from the moment at which the helicoid ring25 and the third external barrel 26 stop moving forward in the opticalaxis direction (i.e., the moment at which the set of three rotationalguide projections 25 b slide into the set of three rotational guidegrooves 13 d from the set of three inclined grooves 13 c, respectively),the set of three roller followers 32 enter the second lead slot portion30 e-3 from the first lead slot portions 30 e-2 of the set of threethrough slots 30 e, respectively, so that the cam ring 31 is furthermoved forward while rotating relative to the first linear guide ring 30.

A rotation of the cam ring 31 causes each of the second lens groupmoving frame 35 and the third lens group moving frame 36, which arepositioned inside of the cam ring 31 and guided linearly in the opticalaxis direction without rotating directly or indirectly by the secondlinear guide ring 33, to move in the optical axis direction with respectto the cam ring 31 in a predetermined moving manner due to theengagement of the set of front cam followers CF3 with the set of frontinner cam grooves CG3 and the engagement of the set of rear camfollowers CF2 with the set of rear inner cam grooves CG2, respectively.In the state shown in FIG. 2 in which the zoom lens 10 is in theretracted state, the third lens frame 42, which is provided in the thirdlens group moving frame 36, has rotated about the pivot shaft 44 to beheld in the radially-retracted position above the photographing opticalaxis Z1 by the position-control cam bar 49, so that the optical axis ofthe third lens group LG3 is moved from the photographing optical axis Z1to the retracted optical axis Z2 that is positioned above thephotographing optical axis Z1. In the course of movement of the thirdlens group moving frame 36 from the retracted position to a position inthe zooming range as shown in FIGS. 1, 22 and 26, the third lens frame42 is disengaged from the position-control cam bar 49 to rotate aboutthe pivot shaft 44 from the radially-retracted position to thephotographing position shown in FIGS. 1, 22 and 26, where the opticalaxis of the third lens group LG3 coincides with the photographingoptical axis Z1 by the sprig force of the torsion coil spring 47.Thereafter, the third lens frame 42 remains held in the photographingposition until the zoom lens 10 is retracted to the position shown inFIG. 2.

Additionally, the rotation of the cam ring 31 causes the first externalbarrel 37, which is positioned around the cam ring 31 and guidedlinearly in the optical axis direction without rotating, to move in theoptical axis direction relative to the cam ring 31 in a predeterminedmoving manner due to engagement of the set of three cam followers CF1with the set of three outer cam grooves CG1, respectively.

Therefore, an axial position of the first lens group LG1 relative to thepicture plane (a light-sensitive surface of the CCD image sensor 12)when the first lens group LG1 is moved forward from the retractedposition is determined by the sum of the amount of forward movement ofthe cam ring 31 relative to the stationary barrel 13 and the amount ofmovement of the first external barrel 37 relative to the cam ring 31, anaxial position of the second lens group LG2 relative to the pictureplane when the second lens group LG2 is moved forward from the retractedposition is determined by the sum of the amount of forward movement ofthe cam ring 31 relative to the stationary barrel 13 and the amount ofmovement of the second lens group moving frame 35 relative to the camring 31, and an axial position of the third lens group LG3 relative tothe picture plane when the third lens group LG3 is moved forward fromthe retracted position is determined by the sum of the amount of forwardmovement of the cam ring 31 relative to the stationary barrel 13 and theamount of movement of the third lens group moving frame 36 relative tothe cam ring 31. A zooming operation is carried out by moving the first,second and third lens groups LG1, LG2 and LG3 on the photographingoptical axis Z1 while changing the distances therebetween. When the zoomlens 10 is driven to advance from the retracted position shown in FIG.2, the zoom lens 10 firstly moves forward to the position shown by anupper half of the zoom lens 10 from the photographing lens axis Z1 inFIG. 1, in which the zoom lens 10 is set at wide-angle extremity.Subsequently, the zoom lens 10 moves forward to the position shown by alower half of the zoom lens 10 from the photographing lens axis Z1 inFIG. 1, in which the zoom lens 10 is set at the telephoto extremity by afurther rotation of the zoom motor 23 in a lens barrel advancingdirection thereof. As can be seen from these sectional views of the zoomlens 10 shown in FIG. 1, the distance between the first and second lensgroups LG1 and LG2 is minimum and the distance between the second andthird lens groups LG2 and LG3 is great when the zoom lens 10 is set atthe wide-angle extremity. When the zoom lens 10 is set at the telephotoextremity, the distance between the first and second lens groups LG1 andLG2 is great and the distance between the second and third lens groupsLG2 and LG3 is small. This variation of the distances among the first,second and third lens groups LG1, LG2 and LG3 for zooming operation isachieved by contours of the set of three outer cam grooves CG1, the setof three rear inner cam grooves CG2 and the set of three front inner camgrooves CG3. In the zooming range between the wide-angle extremity andthe telephoto extremity, the helicoid ring 25 and the third externalbarrel 26 rotate without moving in the optical axis direction. On theother hand, in the same zooming range, the cam ring 31 moves forward andrearward in the optical axis direction while rotating due to theengagement of the set of three roller followers 32 with the second leadslot portions 30 e-3 of the set of three through slots 30 e of the firstlinear guide ring 30.

When the first through third lens groups LG1, LG2 and LG3 are in thezooming range, a focusing operation is carried out by moving the AF lensframe 17, which holds the fourth lens group LG4, along the photographingoptical axis Z1 by rotation of the AF motor 19 in accordance with anobject distance.

Driving the zoom motor 23 in a lens barrel retracting direction causesthe zoom lens 10 to operate in the reverse manner to the above describedadvancing operation to retract the zoom lens 10 as shown in FIG. 2. Inthe course of this retracting movement of the zoom lens 10, the thirdlens frame 42 rotates about the pivot shaft 44 to the radially-retractedposition by the position-control cam bar 49 while moving rearwardtogether with the third lens group moving frame 36. When the zoom lens10 is retracted to the retracted position shown in FIG. 2, the thirdlens group LG3 is retracted into the space radially outside of the spacein which the fourth lens group LG4, the low-pass filter 11 and the CCDimage sensor 12 are retracted as shown in FIG. 2, i.e., the third lensgroup LG3 is radially retracted into an axial range substantiallyidentical to an axial range in the optical axis direction in which thefourth lens group LG4, the low-pass filter 11 and the CCD image sensor12 are positioned. This structure of the zoom lens 10 for retracting thethird lens group LG3 in this manner reduces the length of the zoom lens10 when the zoom lens 10 is fully retracted, thus making it possible toreduce the thickness of the camera body in the horizontal direction asviewed in FIG. 2, i.e., in the optical axis direction.

The structure retracting the third lens group LG3 to theradially-retracted position will be hereinafter discussed in detail. Inthe following description, the terms “vertical direction” and“horizontal direction” refer to the vertical direction and thehorizontal direction as viewed from front or rear of the digital camerasuch as the vertical direction and the horizontal direction of each ofFIGS. 26 and 27, respectively.

As shown in FIGS. 28 and 30, the third lens frame 42 is provided with acylindrical lens holder portion 42 a, a swing arm portion 42 b, acylindrical pivot portion 42 c and an engaging protrusion 42 d. Thecylindrical lens holder portion 42 a directly holds and supports thethird lens group LG3. The swing arm portion 42 b extends in a radialdirection of the cylindrical lens holder portion 42 a. The cylindricalpivot portion 42 c is fixed to a pivot end of the swing arm portion 42b. The engaging protrusion 42 d is formed on the cylindrical lens holderportion 42 a to project in a radial direction thereof on the other end(free end) of the swing arm portion 42 b. The swing arm portion 42 b isprovided with a rear projecting portion 42 e which projects rearward inthe optical axis direction from the swing arm portion 42 b. Thecylindrical pivot portion 42 c is provided with a through-hole extendingin a direction parallel to the optical axis of the third lens group LG3.The third lens frame 42 is provided, in the vicinity of the cylindricalpivot portion 42 c at a position away from the cylindrical pivot portion42 c, with a cam-engaging projection 42 f.

The pivot shaft 44, which supports the third lens frame 42 so as to berotatable about the pivot shaft 44, is inserted in the aforementionedthrough-hole of the cylindrical pivot portion 42 c. Front and rear endsof the pivot shaft 44 are supported by a third lens frame support plate55 (see FIG. 10) and a bearing portion (bearing hole) 36 d of the thirdlens group moving frame 36, respectively. The third lens frame supportplate 55 is fixed to the third lens group moving frame 36 by a set screw56.

The third lens group moving frame 36 is provided, on an inner peripheralsurface thereof at a substantially center thereof in the optical axisdirection, with a central inner flange 36 e. The inner edge of thecentral inner flange 36 e forms an opening 36 f (see FIGS. 9, 10, 22,23, 26 and 27) in which the third lens frame 42 is swingable. Thebearing portion 36 d is formed on the central inner flange 36 e. Thecentral inner flange 36 e is provided below the bearing portion 36 dwith a cam-engaging-projection insertion hole 36 g which extends throughthe central inner flange 36 e in the optical axis direction. The shutterunit 41 is fixed to a front surface of the central inner flange 36 e.The third lens group moving frame 36 is provided, in an internal spacethereof behind the central inner flange 36 e below the photographingoptical axis Z1, with the rotation limit pin 46. The third lens groupmoving frame 36 is further provided on the opposite side of thephotographing optical axis Z1 from the rotation limit pin 46 with aradial opening 36 h which extends through the third lens group movingframe 36 in a direction radially outwards. The radial opening 36 h isformed as a cut-out of the third lens group moving frame 36 in thevicinity of the rear end thereof to be opened on a rear end surface ofthe third lens group moving frame 36.

As shown in FIGS. 9, 23 and 25, the cam ring 31 is provided, on an innerperipheral surface thereof at a position which radially faces the radialopening 36 h in the retracted state of the zoom lens 10, with a radialrecess 31 c which is recessed radially outwards (upwards as viewed inFIG. 27) to correspond to the shape of an outer peripheral surface ofthe cylindrical lens holder portion 42 a of the third lens frame 42, sothat the outer region of the cylindrical lens holder portion 42 a canpartly enter the radial recess 31 c. As shown in FIG. 20, the radialrecess 31 c is formed on a portion of the inner peripheral surface ofthe cam ring 31 on which neither the set of three rear inner cam groovesCG2 or the set of three front inner cam grooves CG3 is formed. In otherwords, the radial recess 31 c is formed on the inner peripheral surfaceof the cam ring 31 within a triangular area thereof behind asubstantially inverted-V shaped portion of one of the three rear innercam grooves CG2 as viewed in FIG. 20. Accordingly, the radial recess 31c is formed on a portion of the inner peripheral surface of the cam ring31 which does not interfere with either the set of three rear inner camgrooves CG2 or the set of three front inner cam grooves CG3. The camring 31 is further provided, on an outer peripheral surface thereof atdifferent circumferential positions in the vicinity of the rear end ofthe cam ring 31, with three external protuberances 31 d which projectradially outwards. The radial recess 31 c is formed on a portion of theinner peripheral surface of the cam ring 31 which corresponds to aninner peripheral surface of one of the three external protuberances 31d. Therefore, portions of the cam ring 31 on which the three externalprotuberances 31 d are formed, respectively, have a sufficient wallthickness, and accordingly, the cam ring 31 secures a sufficientstrength even though the radial recess 31 c is formed on the innerperipheral surface of the cam ring 31. In other words, the cam ring 31can be prevented from increasing in size by forming the radial recess 31c on the portion of the inner peripheral surface of the cam ring 31which corresponds to an inner peripheral surface of one of the threeexternal protuberances 31 d. The three external protuberances 31 d arenot mere reinforcing members, but are also provided on inner peripheralsurfaces thereof with the discontinuous circumferential groove 31 a, andare further provided on outer peripheral surfaces of the three externalprotuberances 31 d with the discontinuous circumferential groove 31 b.Additionally, the three external protuberances 31 d support the set ofthree roller followers 32, respectively.

The third lens frame 42 is supported by the third lens group movingframe 36 therein in a manner such that the cylindrical pivot portion 42c is positioned on the front side of the central inner flange 36 e andthat the cylindrical lens holder portion 42 a projects into the spacebehind the central inner flange 36 e. Due to this structure, the swingarm portion 42 b is provided with a stepped portion 42 g (see FIG. 28)which is stepped in the optical axis direction to extend through theopening 36 f of the third lens group moving frame 36.

Due to such a structure which supports the third lens frame 42, thethird lens frame 42 is rotatable (swingable) about the pivot shaft 44 ina predetermined range of rotation relative to the third lens groupmoving frame 36 and the cam ring 31. Specifically, the range of rotationof the third lens frame 42 ranges from a lower rotation limit at whichthe engaging protrusion 42 d comes in contact with the rotation limitpin 46 to an upper rotation limit at which a portion of the third lensframe 42 comes in contact with a portion of the third lens group movingframe 36. Since the pivot shaft 44 extends parallel to the photographingoptical axis Z1, the third lens group LG3 swings about the pivot shaft44 in the internal space of the third lens group moving frame 36 behindthe central inner flange 36 e while the optical axis thereof remainsparallel to the photographing optical axis Z1 when the third lens frame42 swings.

A coil portion of the torsion coil spring 47 is fitted on thecylindrical pivot portion 42 c of the third lens frame 42, one of theopposite spring ends (a forward-projecting spring end) of the torsioncoil spring 47 is engaged with the swing arm portion 42 b, and the otherspring end (a rearward-projecting spring end) of the torsion coil spring47 is engaged with the central inner flange 36 e. The torsion coilspring 47 biases the third lens frame 42 to rotate about the pivot shaft44 clockwise as viewed in FIGS. 26 and 27. The limit of rotation of thethird lens frame 42 in this biasing direction of the torsion coil spring47, i.e., the photographing position of the third lens group LG3, isdetermined by the engagement of the engaging protrusion 42 d with therotation limit pin 46. The rotation limit pin 46 is formed as arotatable eccentric pin so that the point of engagement of the eccentricpin with the engaging protrusion 42 d can be adjusted by rotating therotation limit pin 46.

The AF lens frame 17, which is positioned behind the third lens groupmoving frame 36, is provided with a forwardly-projecting lens holderportion 17 c, a first arm portion 17 a and a second arm portion 17 b(see FIG. 6). The first arm portion 17 a and the second arm portion 17 bare positioned on radially opposite sides of the forwardly-projectinglens holder portion 17 c. The forwardly-projecting lens holder portion17 c is positioned in front of the first arm portion 17 a and the secondarm portion 17 b in the optical axis direction. The pair of guide holesin which the pair of AF guide shafts 18A and 18B are respectively fittedare formed on the first arm portion 17 a and the second arm portion 17b, respectively. The forwardly-projecting lens holder portion 17 c isformed in a hollow box shape (rectangular ring shape) which surroundsthe photographing optical axis Z1. The forwardly-projecting lens holderportion 17 c is provided on the front end surface thereof with acircular opening in which the fourth lens group LG4 is fitted to befixed thereto. The rear end of the forwardly-projecting lens holderportion 17 c is formed as an open end which is open toward the low-passfilter 11 (see FIGS. 1 and 2).

As shown in FIG. 2, the AF lens frame 17 can move rearward in theoptical axis direction to a point (rear limit for the axial movement ofthe AF lens frame 17) at which the low-pass filter 11 and the CCD imagesensor 12 enter the forwardly-projecting lens holder portion 17 c fromthe rear thereof. Note that since FIG. 2 shows a sectional view throughthe photographing optical axis Z1, the portion of theforwardly-projecting lens holder portion 17 c at such a sectional planeis shown extending rearwards only by a small amount; however, othercircumferential portions of the forwardly-projecting lens holder 17 cextend rearwards sufficient to cover the low-pass filter 11 and the CCDimage sensor 12 in the optical axis direction. Upon the AF lens frame 17moving to this rear limit, a front end of the position-control cam bar49 that projects forward from the CCD holder 14 in the optical axisdirection is positioned in front of the AF lens frame 17 in the opticalaxis direction. As described above, the retracting cam surface 49 a thatlies in a plane inclined with respect to the photographing optical axisZ1 is formed on a front end surface of the position-control cam bar 49,and the radially-retracted-position holding surface 49 b which extendsparallel to the photographing optical axis Z1 is formed on an inner sideedge of the position-control cam bar 49 which extends from theretracting cam surface 49 a (see FIG. 21). The cam-bar insertable hole36 g and the position-control cam bar 49 are aligned in the optical axisdirection so that the position-control cam bar 49 can insert andwithdraw through the cam-bar insertable hole 36 g.

Operations of the third lens group LG3 and other associated elements,which are supported by the above described a structure for retractingthe third lens frame 42 to the radially-retracted position thereof, willbe hereinafter discussed. The position of the third lens group movingframe 36 with respect to the CCD holder 14 in the optical axis directionis determined by a combination of the axial movement of the cam ring 31by the cam diagrams of the set of three front inner cam grooves CG3 andthe axial movement of the cam ring 31 itself. Namely, the third lensgroup moving frame 36 is positioned away from the CCD holder 14 when thezoom lens 10 is moved to the wide-angle extremity, or in the vicinitythereof, as shown by an upper half of the zoom lens 10 in FIG. 1, and ispositioned closest to the CCD holder 14 when the zoom lens 10 is in theretracted state as shown in FIG. 2. The third lens group LG3 isretracted to the radially-retracted position thereof by utilizing theretracting rearward movement of the third lens group moving frame 36from the axial position thereof at the wide-angle extremity to therearmost axial position (retracted position) of the third lens groupmoving frame 36.

In the zooming range between the wide-angle extremity and the telephotoextremity, the third lens frame 42 is held stationary viacontact-engagement of the end of the engaging protrusion 42 d with therotation limit pin 46 by the spring force of the torsion coil spring 47.At this time, the optical axis of the third lens group LG3 is coincidentwith the photographing optical axis Z1 as shown in FIG. 1, so that thethird lens frame 42 is in a photographing position thereof. When thethird lens frame 42 is in a photographing position thereof as shown inFIG. 1, the position control arm 42 f is exposed to the rear of thethird lens group moving frame 36 through the cam-bar insertable hole 36g (see FIG. 26).

Upon the main switch of the digital camera being turned OFF in theready-to-photograph state of the zoom lens 10, the AF motor 19 is drivento rotate in the lens barrel retracting direction to move the AF lensframe 17 rearward, toward the CCD holder 14, to the rearmost position(retracted position) of the AF lens frame 17 as shown in FIG. 2. At thistime, the low-pass filter 11 and the CCD image sensor 12, which aresupported by the CCD holder 14, enter the forwardly-projecting lensholder portion 17 c from the rear thereof to reduce the distance betweenthe fourth lens group LG4 and the low-pass filter 11. Upon the AF lensframe 17 reaching the rearmost position thereof as shown in FIG. 2, thefront end of the position-control cam bar 49 is positioned in front ofthe AF lens frame 17 in the optical axis direction. Supposing that theAF lens frame 17 is not moved to the rearmost position thereofaccidentally, the rear projecting portion 42 e of the third lens frame42 presses the AF lens frame 17 rearward in the subsequent rearwardmoving operation of the third lens frame 42.

Subsequently, the zoom motor 23 is driven in the lens barrel retractingdirection to perform the above described lens barrel retractingoperation. Further driving of the zoom motor 23 to retract the zoom lens10 in the lens barrel retracting direction beyond the wide-angleextremity of the zoom lens 10 causes the cam ring 31 to move rearward inthe optical axis direction while rotating about the photographingoptical axis Z1 due to the engagement of the set of three rollerfollowers 32 with the set of three through slots 30 e (the first leadslot portions 30 e-2 thereof), respectively. As can be understood fromcomparing FIGS. 1 and 2, even though the third lens group moving frame36 is positioned closer to the front of the zoom lens 10 in the opticalaxis direction relative to the cam ring 31 when the zoom lens 10 is inthe retracted position than when the zoom lens 10 is in the wide-angleextremity, the third lens group moving frame 36 comes near the CCDholder 14 when the zoom lens 10 is in the retracted state because theamount of rearward movement of the cam ring 31 relative to thestationary barrel 13 is greater than the amount of forward movement ofthe third lens group moving frame 36 in the cam ring 31 relative to thecam ring 31 in the lens barrel retracting operation.

Further retracting movement of the third lens group moving frame 36together with the third lens frame 42 causes the front end of theposition-control cam bar 49 to enter the cam-bar insertable hole 36 g.The position control arm 42 f is exposed to the rear of the third lensgroup moving frame 36 through the cam-bar insertable hole 36 g asdescribed above, and the retracting cam surface 49 a of theposition-control cam bar 49 which enters the cam-bar insertable hole 36g comes in contact with the position control arm 42 f. The retractingcam surface 49 a of the position-control cam bar 49 serves as a leadsurface which is shaped to produce a component of force making the thirdlens frame 42 rotate about the pivot shaft 44 counterclockwise as viewedin FIGS. 26 and 27 while approaching the position control arm 42 f inthe optical axis direction. Therefore, a rearward movement of the thirdlens frame 42 together with the third lens group moving frame 36 withthe retracting cam surface 49 a remaining in contact with the positioncontrol arm 42 f causes the third lens frame 42 to rotate in a directionto make the engaging protrusion 42 d move away from the rotation limitpin 46 (i.e., in a direction so as to move the cylindrical lens holderportion 42 a upwards) against the spring force of the torsion coilspring 47.

Upon receiving a rotational force from the retracting cam surface 49 a,the third lens frame 42 rotates about the pivot shaft 44 against thespring force of the torsion coil spring 47 from the photographingposition shown in FIGS. 22 and 26 toward the radially-retracted positionshown in FIGS. 23 and 27 in accordance with the retracting movement ofthe third lens group moving frame 36 in the optical axis direction. Uponthe third lens frame 42 rotating to the radially-retracted positionshown in FIGS. 23 and 27, the position control arm 42 f of the thirdlens frame 42 slides on the position-control cam bar 49 from theretracting cam surface 49 a to the radially-retracted-position holdingsurface 49 b to be engaged therewith. In this state where the positioncontrol arm 42 f is engaged with the radially-retracted-position holdingsurface 49 b, the third lens frame 42 is no longer rotated about thepivot shaft 44 in a direction to the radially-retracted position(upwards) by a retracting movement of the third lens group moving frame36 because the radially-retracted-position holding surface 49 b of theposition-control cam bar 49 extends parallel to the optical axis Z1. Atthe same time, the radially-retracted-position holding surface 49 bprevents the third lens frame 42 from rotating in a direction toward thephotographing position by the spring force of the torsion coil spring 47to hold the third lens frame 42 in the radially-retracted position.

As shown in FIGS. 4, 23 and 27, the cylindrical lens holder portion 42 aof the third lens frame 42 enters the radial opening 36 h to partlyproject radially outwards from the outer peripheral surface of the thirdlens group moving frame 36 when the third lens frame 42 is in theradially-retracted position. When the third lens frame 42 is in theradially-retracted position, the cam ring 31 is positioned immediatelyoutside of the third lens group moving frame 36, and the outer region ofthe cylindrical lens holder portion 42 a which partly projects radiallyoutwards from the outer peripheral surface of the third lens groupmoving frame 36 through the radial opening 36 h partly enters the radialrecess 31 c of the cam ring 31.

As can be understood from FIGS. 24 and 25, in the retracted state of thezoom lens 10, the cylindrical lens holder portion 42 a is positionedradially outside of the forwardly-projecting lens holder portion 17 c,and accordingly, the cylindrical lens holder portion 42 a cannot bebrought any closer to the photographing optical axis Z1. Therefore, ifthe radial recess 31 c was not formed on the cam ring 31, it will benecessary for the cam ring 31 to have a greater inner diameter than thecam ring 31 of the present embodiment to prevent the cam ring 31 frominterfering with the cylindrical lens holder portion 42 a of the thirdlens frame 42 when it is in the radially-retracted position. However, inthe present embodiment of the zoom lens 10, in which the third lensgroup LG3 (the cylindrical lens holder portion 42 a) is partlyaccommodated in the radial recess 31 c of the cam ring 31, the innerdiameter of the cam ring 31 and the outer diameter of the third lensgroup moving frame 36 can be reduced by an amount corresponding to theradial depth of the radial recess 31 c. This contributes to thereduction in diameter of the zoom lens 10.

However, the third lens group moving frame 36 that supports the thirdlens frame 42 is a linearly movable member which linearly moves in theoptical axis direction without rotating, whereas the cam ring 31 is arotatable member, and accordingly, the circumferential positions of theradial recess 31 c and the radial opening 36 h about the photographingoptical axis Z1 correspond to each other to prevent the cam ring 31 andthe third lens frame 42 from interfering with each other when thecylindrical lens holder portion 42 a enters the radial recess 31 c ofthe cam ring 31. The present embodiment of the zoom lens 10 is providedwith an idle mechanism (which is composed of the set of three relativerotation allowing grooves 25 f, the circumferential slot portions 30 e-1of the set of three through slots 30 e and the set of three rollerfollowers 32) which prevents the cam ring 31 from rotating even if thehelicoid ring 25 and the third external barrel 26 rotate in an initialstage of the advancing operation of the zoom lens 10 from the retractedstate of the zoom lens 10 as described above. Due to this idlemechanism, when the zoom lens 10 is retracted in the lens barrelretracting direction from the wide-angle extremity, the cam ring 31stops rotating at a predetermined point in front of the retractedposition thereof (at a point before the combination of the helicoid ring25 and the third external barrel 26 rotates by an angle of approximately30 degrees to reach their respective retracted positions), and from thenon the cam ring 31 is linearly moved rearward in the optical axisdirection without rotating. The angle of installation of the cam ring 31is determined so that the circumferential positions of the radial recess31 c and the radial opening 36 h about the photographing optical axis Z1securely correspond to each other in such a non-rotating state of thecam ring 31. Therefore, when the outer region of the cylindrical lensholder portion 42 a partly enters the radial recess 31 c of the cam ring31, a state in which the radial recess 31 c and the radial opening 36 hare communicatively connected to each other in a radial direction of thezoom lens 10 is maintained to thereby prevent the cylindrical lensholder portion 42 a and the cam ring 31 from interfering with eachother.

The structure of the zoom lens 10 which achieves a further reduction inlength of the zoom lens 10 in the retracted state thereof in the opticalaxis direction will be hereinafter discussed in detail. As describedabove, the third lens frame 42 approaches the CCD holder 14 when thezoom lens 10 is retracted to the retracted position. However, the CCDholder 14 is provided with a lens-holder-portion accommodation hole(rear recess) 14 a (see FIGS. 6 and 21) in which the rear end of thelens holder portion 42 a of the third lens frame 42 (the third lensgroup LG3) which has been radially retracted onto the radially retractedoptical axis Z2 can enter. As shown in FIGS. 28 through 30, the lensholder portion 42 a is provided, on an outer peripheral surface thereofin the vicinity of the rear end of the third lens frame 42 at differentcircumferential positions, with three radial projections 42 h whichproject radially outwards. As can be seen in FIGS. 6 and 21, thelens-holder-portion accommodation hole 14 a is shaped to allow the threeradial projections 42 h to enter therein. The CCD holder 14 is providedin the vicinity of the lens-holder-portion accommodation hole 14 a withan engaging-protrusion accommodation hole 14 b which is shaped to allowthe engaging protrusion 42 d of the third lens frame 42 to entertherein. The lens-holder-portion accommodation hole 14 a is formed as abottomed hole, the front end of which (that faces the lens holderportion 42 a of the third lens frame 42 which has been radiallyretracted onto the radially retracted optical axis Z2) is open and therear end of which is closed, and also the engaging-protrusionaccommodation hole 14 b is formed as a bottomed hole the front end ofwhich (that faces the engaging protrusion 42 d of the third lens frame42 which has been radially retracted onto the radially retracted opticalaxis Z2) is open and the rear end of which is closed.

As described above, the shutter unit 41, which is supported togetherwith the third lens frame 42 by the third lens group moving frame 36,includes the set of diaphragm blades S1 and the set of shutter blades S2that is positioned behind the set of diaphragm blades S1 in the opticalaxis direction. The front actuator 41 b for driving the set of diaphragmblades S1 and the rear actuator 41 c for driving the set of shutterblades S2 are disposed on the front side and the rear side of theshutter unit 41, respectively. In the strict sense, only casings of thefront actuator 41 b and the rear actuator 41 c appear in the drawings;namely, the elements of the front actuator 41 b and the rear actuator 41c are accommodated inside the casings. As shown in FIGS. 26 and 27, therear actuator 41 c is located on the shutter unit 41 so as not tooverlap the moving path of the third lens group LG3 that moves between aposition on the photographing optical axis Z1 and the radially retractedoptical axis Z2.

The shutter unit 41 is provided, on a rear surface thereof above thephotographing aperture 41 a, with a lens-holder-portion recess (frontrecess) 41 d (see FIG. 32) in which the front end of the lens holderportion 42 a of the third lens frame 42 which has been radiallyretracted onto the radially retracted optical axis Z2 can enter. Theshutter unit 41 is provided on a rear surface thereof with a retainingplate 41 e which covers and retains the set of shutter blades S2. Thelens-holder-portion recess 41 d is formed as if a part of the retainingplate 41 e were cut out. The range of movement of the set of shutterblades S2 (the internal space of the shutter unit 41 for accommodatingthe set of shutter blades S2) is determined so that the set of shutterblades S2 do not overlap the lens-holder-portion recess 41 d. Inconventional lens shutter type of cameras including a set of diaphragmblades (as exposure control elements) and a set of shutter blades (asexposure control elements) which are provided independently of eachother, it is generally the case that the number of the diaphragm bladesis greater than the number of the shutter blades. Taking this intoaccount, the set of shutter blades S2 are disposed at the back of theshutter unit 41 rather than the set of shutter blades S1, to secure asufficient room for the formation of the lens-holder-portion recess 41 don the back of the shutter unit 41.

In the retracting operation of the zoom lens 10, the third lens frame 42is rotated in a direction toward the radially-retracted position thereofto move the third lens group LG3 from a position on the photographingoptical axis Z1 along the rear surface of the shutter unit 41.Subsequently, the third lens frame 42 (the third lens group LG3) whichhas been retracted onto the radially retracted optical axis Z2 movesrearward together with the third lens group moving frame 36 until therear end of the lens holder portion 42 a enters the lens-holder-portionaccommodation hole 14 a of the CCD holder 14 as shown in FIG. 33. Atthis time, the engaging protrusion 42 d of the third lens frame 42 isaccommodated in the engaging-protrusion accommodation hole 14 b of theCCD holder 14 though not shown in the cross sectional view in FIG. 33.The third lens frame 42 is prevented from moving further rearward by theCCD holder 14 (bottom ends (left ends as viewed in FIG. 33) of thelens-holder-portion accommodation hole 14 a and the engaging-protrusionaccommodation hole 14 b). On the other hand, the third lens group movingframe 36 is designed to be moved slightly rearward even after such aprevention of further rearward movement of the third lens frame 42 bythe CCD holder 14 when the zoom lens 10 is fully retracted. As describedabove, the pivot portion 42 c of the third lens frame 42 is fitted onthe pivot shaft 44, which is fixed to the third lens group moving frame36, to be slidable on the pivot shaft 44 in the axial direction thereof,and the pivot portion 42 c is biased rearward in the optical axisdirection by the compression coil spring 48. Therefore, the third lensgroup moving frame 36 moves rearward in the optical axis directionagainst the biasing force of the compression coil spring 48 relative tothe third lens frame 42 which is prevented from moving rearward (seeFIG. 34). As a result, the front end of the lens holder portion 42 a(the front end of the third lens group LG3) of the third lens frame 42enters the lens-holder-portion recess 41 d of the shutter unit 41 asshown in FIGS. 4 and 34. As can be seen from a comparison between FIGS.33 and 34, the distance M in the optical axis direction between thefront end of the third lens frame 42 (the front end of the third lensgroup LG3) and the bottom end (rear end) of the lens-holder-portionrecess 41 d is smaller in the state shown in FIG. 34 in which the frontend of the lens holder portion 42 a enters the lens-holder-portionrecess 41 d than the state shown in FIG. 33 in which the front end ofthe lens holder portion 42 a is outside of the lens-holder-portionrecess 41 d.

In this manner, the lens-holder-portion recess 41 d is formed on a rearsurface of the shutter unit 41 which is positioned in front of the thirdlens group LG3 (radially-retractable optical element), and the distancebetween the exposure control elements S (the set of diaphragm blades S1and the set of shutter blades S2) and the third lens group LG3 in theoptical axis direction is minimized by bringing the front end of thelens holder portion 42 a to enter the lens-holder-portion recess 41 d,which achieves a reduction in length of the zoom lens 10 in a retractedstate thereof. Moreover, further providing the CCD holder 14 with thelens-holder-portion accommodation hole 14 a and the engaging-protrusionaccommodation hole 14 b, in which portions of the third lens frame 42are allowed to enter, achieves a further reduction in length of the zoomlens 10 in a retracted state thereof.

Although an internal space of the zoom lens 10 in which the third lensgroup LG3 is allowed to move from the photographing optical axis Z1 tothe retracted optical axis Z2 is secured behind the shutter unit 41, thethird lens group LG3 does not fully utilize this space when movingbetween the photographing optical axis Z1 and the retracted optical axisZ2; namely, there are dead spaces which are not utilized for themovement of the third lens group LG3 on opposite sides (left and rightsides as viewed in FIGS. 26 and 27) of the moving path of the third lensgroup LG3. In the present embodiment of the zoom lens 10, the rearactuator 41 c is positioned in one of the two dead spaces (specificallythe right space as viewed in FIGS. 26 and 27). This arrangement of therear actuator 41 c improves the utilization factor of the internal spaceof the zoom lens 10, thus contributing to reduction in length of thezoom lens 10 in a retracted state thereof.

Although the above discussion has been addressed to the above describedembodiment of the retractable lens system, the present invention is notlimited solely to this particular embodiment. For instance, although thethird lens group LG3 (radially-retractable optical element) retracts toa position off the photographing optical axis Z1 by rotating about thepivot shaft 44, the present invention can be applied to a different typeof retractable lens system in which the radially-retractable opticalelement retracts to a position off a photographing optical axis bymoving linearly.

Although in the above-described embodiment the diaphragm blades S1 andthe shutter blades S2 are both provided as exposure control elements,the exposure control element(s) can be either a diaphragm blade(s) or ashutter blade(s).

Although the above illustrated embodiment of the retractable lens systemis a retractable zoom lens, the present invention can be applied to anytype of retractable lens system which can change between aready-to-photograph state and an accommodated state (retracted state),and is not limited solely to a retractable zoom lens.

Obvious changes may be made in the specific embodiment of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

1. A retractable lens system comprising: a linearly movable ring whichis guided linearly in an optical axis direction of a photographingoptical system, and retracts when said retractable lens system changesfrom a ready-to-photograph state to a retracted state; aradially-retractable optical element of said photographing opticalsystem, said radially-retractable optical element being supported bysaid linearly movable ring to be retractable to a radially-retractedposition outside of said optical axis from a ready-to-photographposition on said optical axis; an exposure control unit which includesexposure control elements, and is supported by said linearly movablering to be positioned adjacent to said radially-retractable opticalelement in said optical axis direction; an exposure control unit recessformed on said exposure control unit to face said radially-retractableoptical element when said radially-retractable optical element is insaid radially-retracted position, and a retracting device which retractssaid radially-retractable optical element from said ready-to-photographposition to said radially-retracted position along said exposure controlunit and brings at least a part of a frame of said radially-retractableoptical element to enter said exposure control unit recess when saidlinearly movable ring retracts from a ready-to-photograph position to aretracted position.
 2. The retractable lens system according to claim 1,wherein said radially-retractable optical element is positioned behindsaid exposure control unit, and wherein, when said linearly movable ringretracts from said ready-to-photograph position to said retractedposition, a support frame which supports said radially-retractableoptical element comes into contact with a stationary member positionedbehind said radially-retractable optical element to be prevented fromfurther moving rearward, and said exposure control unit approaches saidradially-retractable optical element to bring said at least a part ofsaid frame of said radially-retractable optical element to enter saidexposure control unit recess.
 3. The retractable lens system accordingto claim 2, wherein said support frame, which supports saidradially-retractable optical element, is rotatable about a pivot betweensaid ready-to-photograph position and said radially-retracted position,said pivot being fixed to said linearly movable ring to extend parallelto said optical axis, and wherein said support frame is movable alongsaid pivot in a direction parallel to said optical axis.
 4. Theretractable lens system according to claim 2, wherein said retractingdevice comprises a stationary cam bar which projects from saidstationary member and includes a cam surface for converting a movingforce of said linearly movable ring in said optical axis direction intoa moving force in a direction orthogonal to said optical axis direction.5. The retractable lens system according to claim 2, wherein saidstationary member, which is positioned behind said radially-retractableoptical element, includes a stationary member recess formed on a frontsurface of said stationary member to be aligned with said exposurecontrol unit recess of said exposure control unit in said optical axisdirection, and wherein at least a rear end of said radially-retractableoptical element is accommodated in said stationary member recess of saidstationary member when said retractable lens system is in said retractedstate.
 6. The retractable lens system according to claim 1, wherein saidexposure control unit comprises an actuator for driving said exposurecontrol elements, and wherein said actuator is positioned on a same sideof said exposure control unit as said exposure control unit recess so asnot to overlap a moving path of said radially-retractable opticalelement.
 7. The retractable lens system according to claim 1, whereinsaid exposure control elements comprise at least one diaphragm blade andat least one shutter blade which lie at different respective positionsin said optical axis direction, said shutter blade being positionedcloser to one of front and rear surfaces of said exposure control uniton which said exposure control unit recess is formed than said diaphragmblade.
 8. The retractable lens system according to claim 1, wherein saidphotographing optical system comprises a zoom lens system.
 9. Theretractable lens system according to claim 1, wherein saidradially-retractable optical element is positioned between a frontmostoptical element and a rearmost optical element of said photographingoptical system in said optical axis direction.
 10. The retractable lenssystem according to claim 1, wherein said radially-retractable opticalelement comprises a lens group among a plurality of movable lens groupsof said photographing optical system.
 11. The retracting lens systemaccording to claim 2, wherein said retracting lens system isincorporated in a digital camera using an image pickup device, andwherein said image pickup device is mounted to said stationary member.12. The retractable lens system according to claim 1, further comprisinga cam ring, positioned around said linearly movable ring, for moving aplurality of optical elements of said photographing optical system whichinclude said radially-retractable optical element in said optical axisdirection when said cam ring is rotated.
 13. A retractable lens systemof a camera, comprising: a linearly movable ring which is guidedlinearly in a optical axis direction and retracts when said retractablelens system changes from a ready-to-photograph state to a retractedstate; a lens group supported by said linearly movable ring to beretractable to a radially-retracted position outside of said opticalaxis from a ready-to-photograph position on said optical axis; anexposure control unit which includes shutter blades, and is supported bysaid linearly movable ring to be positioned adjacent to said lens groupin said optical axis direction; a stationary member positioned behindsaid lens group; a retracting member which projects from said stationarymember, and retracts said lens group from said ready-to-photographposition to said radially-retracted position along said exposure controlunit by a force produced by a relative movement between said linearlymovable ring and said retracting member in said optical axis directionwhen said linearly movable ring retracts from a ready-to-photographposition to a retracted position; and an exposure control unit recessand a stationary member recess which are formed on a rear surface ofsaid exposure control unit and a front surface of said stationary memberto face a front end and a rear end of said lens group, respectively,when said lens group is in said radially-retracted position, whereinsaid lens group retracted to said radially-retracted position and saidexposure control unit move rearward and approach each other in saidoptical axis direction to bring a front end and a rear end of said lensgroup to enter said exposure control unit recess and said stationarymember recess, respectively, when said linearly movable ring retractsfrom said ready-to-photograph position to said retracted position. 14.The retractable lens system according to claim 1, wherein no photographcan be taken in said retracted state.
 15. The retractable lens systemaccording to claim 1, wherein said radially-retractable optical elementand said exposure control unit are eccentric to each other in saidretracted state.
 16. The retractable lens system according to claim 13,wherein no photograph can be taken in said retracted state.
 17. Theretractable lens system according to claim 13, wherein said lens groupand said exposure control unit are eccentric to each other in saidretracted state.